光圈数 meaning in English

f-number
fn
stop number

E - photographic lenses ; exposure stop e - stop
照相镜头.爆光的光圈数
Photographic lenses - methods for the measurement of the effective aperture , f - number and relative aperture
摄影镜头.有效孔径光圈数和相对孔径的测量方法
For underexposed pictures , set a large aperture ( smaller number aperture setting ) or slower shutter speed . for overexposed pictures , set a smaller aperture ( large number aperture setting ) or faster shutter speed
对于曝光不足的景物,可适当增加光圈（较小的光圈数）或选用较慢的快门速度。